: The specific aim of the proposed study is to validate a new method of measuring regional organ blood flow using non-radioactive, stable-labeled microspheres assayed by neutron activation (NA) analysis. The proposal is based on the hypothesis that stable-labeled research products introduced into a biological matrix can be accurately and rapidly assayed using NA. This technology will provide a cost-effective method for reducing the production of low-level radioactive waste generated from biomedical research. The long-term goal is to develop additional research products based on the NA technology, which could be used in applications where current non-radioactive methods are labor-intensive and less effective. Phase I of the proposed project is an in-house alpha test which will directly compare stable-labeled microspheres to a co-injection of radiolabeled microspheres in an in vivo rabbit model of coronary occlusion and reperfusion. Statistical analysis will be used to assess agreement between the two methods, thereby supporting the working hypothesis and demonstrating feasibility. Phase I will also provide important design parameters for an automated activation and counting system to be constructed during Phase II. This automated system will be able to assay the large numbers of samples necessary for commercial operation. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE